This invention relates generally to data communications and particularly to providing relatively high speed serial communications between a receiver and a transmitter.
A variety of techniques exist for enabling a receiver and a transmitter to settle on a data communication rate between the two devices. For example, in technology currently used with 56K telephone modems, the transmitter starts at a lower data rate which is guaranteed by an applicable specification to be acceptable to the receiver. After communications have been initiated, the transmitter may step up the data rate if possible. Similarly, if in the course of data communications the receiver begins to perceive that the error rate is too high, the receiver may request that the transmitter lower the data rate. In this situation, the data communications are established at a relatively lower speed rate and then, in the course of communications, the rate may be increased or decreased.
One problem that arises in establishing the desired data rate is that prior to the establishment of the communication channel, the available communications between the receiver and the transmitter are particularly limited. This means that the receiver is unable to provide very much information to the transmitter about its ability to handle the data being provided by the transmitter until after communications have been established. This may explain why the protocol described above in connection with 56K telephone modems is utilized.
Another problem that arises in establishing the data communication rates between a transmitter and a receiver is that while the devices may have a nominal or specification data transmission rate, particular circumstances may arise at any given point in time that may change the ability of the devices to proceed at the nominal rate. For example, the receiver may be experiencing considerable line delays at a particular point in time because of operations going on at the receiver. Similarly, other conditions may affect the ability to communicate at the nominal rate. Existing techniques generally set a desired rate and only adjust that rate if, after communications have been established, it is determined that the error rate is unbearably high. Of course, this is the situation of xe2x80x9ctoo little, too latexe2x80x9d because the communications have already been impaired.
Thus, it would be desirable to have a communication protocol which enables communications to proceed at the highest possible rate as soon as possible and which accounts for the conditions which may exist at any given point in time when a communication is being initiated.
In accordance with one embodiment of the present invention, a method includes transmitting a predetermined data pattern to a receiver at a first data rate. If the receiver does not recognize the pattern, the pattern is transmitted at a second data rate that is lower than the first data rate.
Other aspects and advantages are set forth in the accompanying detailed description and claims.